Generally, a heating system, having been applied to residential buildings, such as houses, villas, and apartments, employs a structure involving a wet heating process, in which a pipe, laid under a flooring material of a room in a building, is supplied with heating fluid, such as hot water, thereby heating the room of the building. However, such a wet type heating system has a lower heating efficiency, resulting in severe thermal loss, and requires lengthy concrete curing, resulting in extended construction time. Furthermore, upon leakage of water from the pipe, a mortar layer of the heating system must be broken for repair, thereby impeding easy overhaul while increasing overhaul costs.
In order to solve the problems of the conventional wet heating system as described above, a dry heating panel, made of concrete, a synthetic resin or yellow clay was developed. A pipe is embedded within the dry heating panel for carrying heating fluid therein or the dry heating panel is provided with grooves or fixing members for inserting the pipe for carrying heating fluid. The dry heating panel is an assembly heating panel, and has advantageous effects in that the construction of the heating system may be completed by simply assembling prefabricated pieces of the dry heating panel, thereby reducing construction time, and simplifying maintenance and overhaul operations thereof. However, the dry heating panel has problems in that, since it adopts a line heating structure in which heat is concentrated where the pipe for carrying heating fluid is located, generating a severe temperature variation in the heating system, the dry heating panel is ineffective in view of heating efficiency, and in that, since the pipe itself is made of metal or a synthetic resin, it is expensive, resulting in increased construction costs. Furthermore, thermal loss may occur on the pipe, and a dewing phenomenon may occur on the surface of the pipe, thereby wetting the panel.
In order to solve the problems of the conventional dry heating panel described above, as disclosed in U.S. Pat. No. 5,080,166 and Korean patent application Laid-open publication No. 2002-95733, a plate-shaped heating panel comprising an inner fluid pathway formed therein to allow the heating fluid to flow therethrough was developed. Compared with the dry type heating system adopting the line heating structure, the plate-shaped heating panel having the inner fluid pathway therein adopts a planar heating structure in which the heating fluid flows not in a local area but in an overall area of panels. Thus, the plate-shaped heating panel provides very high heating efficiency, resulting in reduction of fuel expenses, and it does not require installation of the pipe, thereby eliminating a complicated piping process and reducing the piping expenses. Additionally, the plate-shaped heating panel is not subject to thermal loss and the dewing phenomenon, which usually occurs on the surface of the pipe in the structure of the dry heating panel, and allows a weight of the panel to be reduced. Furthermore, the plate-shaped heating panel is very easy to construct and repair.
Conventionally, the plate-shaped heating panel with an inner fluid pathway formed therein was formed by way of blow molding, also known as hollow molding. The blow molding is a molding method in which a hollow product is formed by blowing air into a separating mold, in which molten thermoplastic forming material is inserted and then softened with heat. More specifically, the blowing molding fundamentally comprises three steps, namely a) preparing a parison or a preform previously formed from a plastic resin into a tube shape, b) positioning the parison in a cavity of the mold and blowing air into the parison to expand the plastic resin until the plastic resin reaches a wall of the closed mold, and c) curing the plastic resin, followed by ejecting a final product by opening the mold.
However, when manufacturing the plate-shaped heating panel comprising the inner fluid pathway formed therein by using the blow molding, since hot air is blown into the parison with non-uniform pressure, which is a characteristic of the blow bolding, areas of upper, lower, right and light sections of the fluid pathway are different in the final heating panel. In addition, when the pressure of the air is lower than a desired pressure or the fluidity of the molten resin is increased, some portion of the fluid pathway can be blocked to cause non-uniform flow of the heating fluid in the heating panel and variation in thickness of upper and lower plates of the heating panel.
When the non-uniform flow of the heating fluid and the variation in thickness of the upper and lower plates of the heating panel occur, heating performance of the panel is deteriorated. In other words, variation in temperature can occur on the floor of the room, it takes a long time to heat the room to a predetermined temperature, and the speed of the heating fluid is lowered due to resistance applied to the heating fluid in the heating panel.